Printing telegraph system



Oct. 27, 1936. 1 E 2,058,398

PRINTING TELEGRAPH SYSTEM Filed July 16, 1934 2 Sheets-Sheet 1 'Oct. 27, 1936. s. z. BEAR PRINTING TELEGRAPH SYSTEM 2 Sheets-Sheet 2 Filed July 16, 1934 F -mm l nm HIWEMIF 1 1 1 H H H 7172 73 75 Mun r n nm ggh m r n nm rfimm mmwimn w g r wrfim [aw-M M m m I 106 INVENTOR. 109 109 106 107 107 107 .107-I:| I08 108 Patented a. 27, 1936 UNITED STATES PATENT OFFICE 8 Claims.

(Granted under the act of March 3, 1883, as amended April 30, 1928; 370 0. G. 75'!) This invention relates to improvements in printing telegraph systems and the like, and more especially to communication systems of the printing telegraph type using either wire or radio between stations.

The objects of the invention are to provide a system by which printed characters may be produced by an electrical typewriter operated by a remote key-board; to provide a system by which alternating currents of audio frequency may be used as an actuating medium; to provide a system for translating the double signal into a type-bar actuating impulse; to provide a system by which two or more signals of different frequency may be used for each character transmitted;- and to provide a system employing means for sending out a double signal impulse by a key .movement. While the character of the system herein disclosed may be embodied in various forms or arrangement of structure, the invention may be understood best by reference to the one preferred form as shown in the drawings which are a part of this application and of which the Figure 1 shows a key-board connection to the oscillators and amplifier; the Figure 2 illustrates a detail of a key mechanism in normal position; the Figure 3 illustrates the same key mechanism in partially depressed position; the Figure 4 illustrates the same key mechanism in a wholly depressed position; the Figure 5 shows the connection between the selecting circuits and the type-baroperating solenoids; the Figure 6 is a schematic arrangement of a line connected system; and the Figure 7 is a diagrammatic arrangement for a radio or wireless system, the Figures 1 to 4, both inclusive, having reference to the transmitting apparatus of the system, while the Figure 5 refers to the receiving apparatus thereof.

Referring more particularly to that part of the accompanying drawings relating to the transmitting apparatus, the key mechanism I, as illustrated by the Figure 2, is one of several like key mechanisms with which asingle key-board may be provided, said key mechanism being provided with the key IA fixed to the resilient leaf 3 of the combination of resilient leaves 2, 3, 4, 5 and 6,

the leaf 8 however may be rigid if desired, these leaves being secured together adjacent one end, as at X, by means of the insulation material XA and thereby insulated and spaced, each one from the others, in parallel relation. The contact 1 comprises the normally interengageable projections with which the leaves 2 and 3 are provided. The contact 8 comprises the normally interengageable projections with which: the leaves 4 and 5 are provided. The contact '9 comprises the projections normally relatively spaced and with which the leaves 3 and 5 are provided. The leaves 2, 3, 4, and i are provided with the ter- 5 minals 2A, 3A, 4A, and GA, respectively, and the entire key mechanism I is provided with the support KB having the attaching means XC by which the key mechanism may be mounted in erect position upon a frame or platform (not illus- 10 trated) The key mechanism I, above described is intended to be supplied in sufllcient quantities to equip a frame, or platform of a transmitting apparatus with multiple rows, such as H, l2, l3; and I4, of said key mechanisms, as shown in the 15 Figure 1, the twelve key mechanisms of the row II, for instance, being designated as the key mechanisms IS, I6, l1 ,l3, I9, 20, 2l, 22, 23, 24, 25, and 26. The key mechanisms of each of the several rows H to 14 are connected inseries, the terminal 3A of the leaf '3 of each of the mechanisms 15 to 26 is connected to the terminal 2A of the leaf 2 of each succeeding mechanism in the row I I by means of the line 33, while the terminal 24 of the leaf 2 of the mechanism is 25 is connected by means of the line 2B"to an os cillator the location of which is at '40, and the terminal 3A of the leaf 3 of the mechanism 26 is connected by means of the'line 30 to the ter-,

minal 2A of the leaf 2 of the mechanism ISA in 30 the next row l2. The terminals 4A of the leaf 4 of the several mechanisms ii to 26 of the row II, and also of the rows l2, l3 and I4 are each connected by means of the lines 43 and 40 to .the tap leads 216 which are brought out from the primary winding 21A of the inductance coil 21, the capital shift key .3, with its mechanism hereinafterexplained, being inserted in these lines 4C, this shift key 82 being designated by symbol in the Figure 1, its spring arms 83A being in neutral positions. The terminal A of the leaf 6 of each of the key mechanisms I! to 26 of the several rows or groups H to l4 having a common connection, by means of the lines 613, 6C and 6D, with the right-hand end of the primary 5 winding 21A of the inductance coil 21, the tuning condensers 23 to 39, respectively, being inserted in the lines 63.. The left-hand end of the primary winding 21A is connected, by means of the line 21D, to the spacing oscillator at 40, said oscillator being connected, by means of the line 40A, to the terminal 3A of the'leaf 3 of the ke' mechanism 230 and also to the grid of the amplifier tube a by means of the line ms, the fixed condenser 4IJ being inserted in the last mentioned line. The left-hand end of the secondary winding 21B of the inductance coil 21 is connected, by means of the line 21D, to the grid of the oscillator tube 4|, a resistor MC being inserted in this connection, while the right-hand ends of both primary and secondary windings 21A and 21B of the inductance coil 21, and the minus side of the B power supply, are connected, by means of the lines 4 IA and MB, to the cathode of the tube 4|, a resistor MD being inserted in the line MB. The plate of said tube 4| is connected, by means of the line ME to the plus end of the B power supply, a resistor MF being inserted in the line ME. The line MG connects ME from said plate to the grid of the amplifier tube 43, a variable resistor MH, together with fixed condensers MI and MJ upon either side thereof, being inserted in the line MG. At this grid connection-line 4|G there is also a line connection by means of the line MK to the minus side of the B power supply, a resistor ML being inserted in this last mentioned line adjacent the grid of the tube 43. Also from the minus side of the B power supply there is the connecting line 43A to the cathode of the tube 43, a by-pass condenser 43C shunted by a resistor 433 being inserted in said line 43A. The plate of the amplifier tube 43 is connected by means of the line 440 to the upper end of the primary winding 44A of the output transformer 44, while the lower end of said primary winding 44A is connected by means of the line 44D to the plus side of the B power supply, said lower end of the primary winding 44A being also connected by means of the line 44D to the cathode of the tube 43, the fixed condenser 44E being inserted in this last mentioned line. There is a connection by means of the line 480 from the minus side of the "3 power supply to the spacing oscillator at 40. The ends of the secondary winding 44B of the transformer 44 are connected by means of the lines 44F and 44G to the transmission'circuit which transmits to the receiving apparatus hereinafter explained. The above described structure is thus grouped and connected to provide a transmitting apparatus having a multiple combination of key mechanisms in groups and sub groups; a tuning circuit comprising the condensers 28 to 39 and the induction coil 21; the oscillator tube 4| and the amplifier tube 43 with coupling resistances and fixed condensers and resistors; the place 40 reserved for a tube with coupling resistance and necessary fixed condensers and resistors similar to that of the tube 4|; an output transformer 44; a B power supply having a transformer, rectifier tubes, necessary condensers and choke-coils for a filter system; and a shift-key double throw four-pole switch mechanism 83. I

' Referring to that part of the drawings relating to a receiving apparatus of this improved system, the three primary coils 46, 60, and 19, as illustrated by the Figure 5, are connected in parallel, the lines 45 and 45A both designate the input circuit of the receiver and connect the said coils 46, 66, and 19 in parallel relation. These primary coils 46, 60, and 19 are so relatively placed as regards the secondaries 41, 6|, and 80, respectively, that they are inductively coupled to transferenergy from the input circuit to the tuning circuit. While these primary and secondary coils are illustrated in single sets, it is to be understood that, of the group relay, consisting of parts 46, 41, 48, 49, 50, and 5|, there are in aft eight, of such relays, and of the character relays, consisting of parts 60, 6| 62, 63, 64, 65, and 18, there are in all twelve relays, and of the special relay, consisting of parts 19, 80, 8|, 9|), 9|, and 92,there is but one relay, and of the ordinary relay 93 there is but one relay. Besides the primary and secondary windings 46 and 41, the group relay comprises the thyratron tube 49 the grid of which is connected by means of the line 41A to the upper endof the secondary winding 41, while the cathode of the tube 49 is by means of the line 413 grounded at 41C. The lower end of the secondary winding 41 is connected by means of the line 41D to the ground line 41B, the battery 50 being inserted in the line 41D, and the by-pass condenser 5| also being placed in parallel with said battery 50, a tuning condenser 48 being inserted in parallel with the secondary winding 41 by means of the line 48A connecting the line 41A with the line 41D adjacent the lower end of the secondary winding 41. The plate of the gas tube 49 is connected by means of the line 49A to the lower end of each of the solenoids 66, 61, 68, 69, 16, 1|, 12, I

.line 6 IA t0 the upper end of the secondary winding 6|, while the cathode of the tube 63 is connected by means of the line 6|B to the upper portion of each of the solenoids 1|, 1| A, 1 B, 1 C,

1|D, 1|E, HF, and HG in the rows 52, 53, 54, 55, 56, 51, 58, and 59, respectively. The lower end of the secondary winding 6| is connected by means of the line 6| C to the line 6|B, the battery 64 being inserted in the line BIG and the by-pass condenser 65 being placed in parallel with the said battery 64, the condenser 62 being inserted in parallel with coil 6| by means of the line 62A connecting the lines 6|A and 6| C. The plate of the gas tube 63 is connected by means of the line 63A to the line 493. Besides the primary and secondary windings 19 and 80, respectively, the single set of special relay comprises the ordinary vacuum tube 8| the grid of which is connected by means of the line A to the upper end of the secondary winding 86, while the oathode of the tube 8| is connected by means of the line 8|A to the resistor 9|. The lower end of the secondary winding 80 is connected by means of the line 80B to the line A which connects the line 80A to the line 86B and is grounded at 800, the line 96A having inserted therein the condenser 90 in parallel with the secondary winding 86, and the by-pass condenser 92 being connected by means of the line 92A to the lines 90A and 8| A and in parallel with the resistor 9|. The plate of the vacuum' tube 8| is connected by means of the line 93A to the ordinary relay 93. The relay 93 has a connection, as at 93B, with the plus side of a B power supply, the minus sideof said B power supply being grounded as at 93C. The above described structure is thus grouped and connected to provide the improved system with one or more receiving apparatus, each apparatus comprising actuating relays selectively giving energy to solenoids which operate typebars.

In the normal at-rest position of the key mechanism illustrated by the Figure 2, the contact 1 is closed while the contacts 9 and I0 arev open. 75

The contact 8 has no electrical significance excepting through the contact 9.

Preparatory to the operation of the keys IA of the transmitting apparatus, the apparatus is connected to a source of electrical energy conducted into the circuit which includes the contact I and the terminals 2A and 3A of the several key mechanisms in series. In each key mechanism the contact I is normally closed to establish said circuit as a spacing circuit which energizes the oscillator at 40 to send out a frequency impulse to automatically operate a spacer in the receiving apparatus which is in tune with said frequency impulse, the plate current in the spacer frequency tube 8| dropping to zero, and the relay 93 in its plate circuit closing the contacts which feed current to the thyratron tubes 49 and 63. These tubes are thus made ready to be operated by the excitation of their respective grids.

Each manually or otherwise operated key mechanism I has a multiple function:

A slight downward movement of any selected key IA opens the contact I of that particular.

key mechanism and interrupts and suspends the spacer frequency impulse during the further downward movements of the said key IA.

A further downward movement of the said key IA closes the contact 9, the contact 8 remaining closed and the closed contact 9 (through the medium of the closed contact 8) completing a group frequency circuit which includes the terminals 3A and 4A of the leaves 3 and 4 of the operated key mechanism, and, with turns in the inductance coil 21 short-circuited by the particular tap connection, the proper resonance of the particular group frequency will occur and oscillation of that frequency will be sent out to the receiving apparatus.

A slightly further downward movement of the said key IA will open the contact 8 to break the group frequency oscillator circuit, but will not affect the relay at the receiving apparatus because the grid cannot stop the plate current of a thyratron tube.

A final and complete downward movement of the said key IA will close the-contact III to establish the individual character circuit which includes the terminals 3A and 6A of the operated key mechanism, said circuit also including a particular one of the condensers 28 to 39 which tunes the oscillator M to a particular frequency. The inductance for this frequency is always the same and is in circuit at all times. At the receiving apparatus the oscillator of theindividualcharacter frequency wili-operate the proper group relay tube.

Upon the release of the thus operated key IA, the individual character frequency relay is stopped, but the thyratron action of the relays holds the type-bar solenoid in action and, while the group frequency circuit (through contacts 8 or 9) thereby will be closed and opened again, no change occurs because of said thyratron action which holds the solenoid circuit closed until the plate current is interrupted. A full return of the key IA of the operated key mechanism to its normal at-rest position, the contact 1 is made to close-the spacer circuit whereupon the spacer frequency signal is sent to the receiving apparatus where this oscillation will operate the special relay which operates to open, the plate circuit of the distant receiver.

It will be noted that no synchronizing means are used with my invention and the various troubles encountered with this class of apparatus are limited. If precautions are taken to avoid interference caused by beat frequencies of substantially the same frequencies as the regular signal, the simultaneous transmission. ofthe group and individual frequencies may be used with greater speed of transmission. Instead of the eight groups as shown, arrangements may be used to shift the type-bars as in the ordinary typewriter and a smaller number of frequencies oniywill be necessary.

The invention above described includes a keyboard, multiple switches, each actuated by a key mechanism, and an oscillator 4| whose frequency is changed by the selective operation of these key mechanisms, the successive pulses of different frequencies being amplified by the vacuum tube amplifier 43 and sent over a line to the receiving apparatus or used to modulate a carrier frequency which is also sent over a wire line to The initial pulse may also be used to modulate a high or radio frequency wave and antenna used to transmit the message to the receiver by broadcasting.

If a wire line is used to transmit the massage, either directly or by the use of a modulatedcarrier frequency, then amplifying repeaters may be used to keep the signals at .proper strength throughout the line to avoid interference with other lines or the picking up of extraneous signals.

At the receiving station, which may be one of several which pick up the message at one and the same time, the signals are brought back to their original form by the wellknown means and are impressed on the input circuits of several discharge tube relays. Each of these input circuits is tuned to one of the several frequencies used. The tube whose input circuit is tuned to the particular frequency being transmitted at the moment will have its grid swung sumciently positive by the combined 'action of bias and signal that the plate current will flow therein.

With any ordinary form of communicating systems it is necessary to use sharply tuned input circuits if any large. number of characters are to be transmitted within a narrow band of frequencies. For straight wire transmission the cost of line structure and maintenance is proportioned to the band width transmitted. For carrier current work multiple use. of a line is limited by the band width and it is therefore essential that the number of different frequencies used be cut down to the limit. For reasonable quality the number of characters required will be thirty-five and the same number of separate frequencies will be required. For better quality of the printed output more characters would be used with either a broader band of frequencies ormore crowding together of those used. In any case, a-system which uses less frequencies is to be preferred.

In this improved form of printing telegraph systems two frequencies are used for each character. These two' frequencies are not transslight time interval between them, as timed by the operation of the key mechanisms as-already explained. I do not intend to disclaim the simulmitted simultaneously but preferably with a taneous transmitting'of the two frequencies, but 1 do point out that in this case the beat frequencies of the two signals must be arranged as to not interfere or operate as other characters;

In the improved form the characters are arranged in rows or groups in the same manner as the keys of a typewriter. The first of the two frequencies transmitted upon the partial operation of a key will select the group and the second of said two frequencies upon a full operation of said key will determine the number or position of the characters in the group. In this way a much smaller number of frequencies will be required; for instance, for one hundred characters one hundred frequencies would be requiredin the ordinary form of system, but in the improved form the characters may be divided into ten groups of ten characters each and only twenty frequencies will be required with a saving of eighty percent of the band width.

Instead of the two successive frequencies a larger number could be used. If five main groups were used, with five subgroups and five characters per group, then one hundred and twenty-five characterscould be produced with fifteen frequencies with a saving of about ninety percent of the band width used when a. single frequency is used for each character. Greater savings will be found with more successive impulses per character, but the speed of transmission would be reduced and probably balance any gain in reduction on band width.

For high quality of output all the letters of the alphabet would be required twice. One for capital letters and another for each small letter, making in all fifty-two characters. Ten numerals and about twenty-four punctuation marks and special characters, as are commonly used on the standard typewriter, would also be required. In addition, other signals are required for the proper automatic operation of a typewriter, such as carriage return, carriage positioning, line spacing, word spacing, etc.

Provision has been made in the improved form, as above described, for ninety-five different oper-- ations to be performed by twenty different frequencies by using eight groups, of which six are used with twelve frequencies per group, and each of the remaining two groups with eleven frequencies, thus providing for ninety-five operations, the ninety-fifth operation being the controlling means of the special spacer frequency already explained. Of course a more elaborate system easily could be used having more groups or more characters per group and also a more simple arrangement could be used having less groups or less characters per group.

After suitable amplification or modulation successive impulses of audio frequency are sent over an intervening medium, such as a wire line or space between two antennae.

At the receiving apparatus the signals are demodulated if necessary and amplified to a standard value and impressed on a series of parallel connected coils 46, 60, and 19 which act as primaries to a number of tuned circuits. The number of these tuned circuits correspond to the number of different frequencies used in the system. Each tuned circuit is shunted across the input of a gas or vapor-filled hot cathode tube of the thyratron type, except one circuit which has a vacuum-type amplifying tube instead of a. thyratron tube. This special tube and circuit is used for spacing, as has already been explained.

These tuned relays are arranged and connected so that the plate current of those tuned to the group frequencies are connected to the cathodes of those tuned to the individual character frequencies through a series of solenoids which actuate the type-bars of a typewriter. One connection of each solenoid in a group is connected to a group line A which in turn is connected to the plate of the tuned group relay. The other connection of the solenoid is made, by means of the line 6| B, to the cathode of the tuned character relay, the same relative position in the group being connected to the same cathode. For the improved system there will be eight group relays and twelve individual character relays.

The high resistance 18 is shunted across the solenoid and individual character relays, preferably one from each group relay plate to the common plate end of the individual character relays. This resistance enables the voltage to be applied to the group tubes regardless of whether the individual character tubes are excited or not. During the operation, as already explained, the group frequencies are sent first for every signal and the proper tuned circuit will respond and swing the grid of the associated tube far enough positive to let the plate current flow. When this part of the signal stops, due to the final key movement already explained, the plate current does not stop because of the peculiar property of thyratrontubes which enables the plate current to flow regardless of the grid potential after once starting. The second impulse of the signal will set one of the individual character relay tuned circuits in resonance and swing its grid far enough to start the plate current. This action completes the circuit and the solenoid will actuate the proper type-bar. Upon release of the key nothing happens during the first phases of upward key movement wherein the group and individual character frequencies are stopped and started again because the thyratron action of the tubes used will keep the circuit closed regardless of the grid excitation as already explained. When the key reaches its normal position however a frequency impulse is sent out which resonates with the special relay using the vacuum-type amplifier tube 8| and this relay actuates the ordinary relay 93 opening the plate circuit. The solenoid then releases the type-bar.

For special operation, such as line spacing, any proper mechanical device may be actuated instead of the type-bar, but the sequence is the same. or course, when the key is initially pressed, the special spacing relay circuit is broken because a thyratron tube is not used in this case and the loss of grid excitation will stop the plate current as this tube is biased at the plate current cut-off point. If sufficient energy to operate the relay is not obtained, then other tubes connected in cascade may be used to increase the output to the desired point.

I have found that about three cycles of operation are necessary to complete the action in the most unfavorable cases and as the lowest frequency used will be of the order of two hundred and fifty cycles per second and two sets of impulses are required per character, the time for characters will be of the order of one-fortieth of a second for the longest signal. Allowing the same time for key return as for depression a total of one-twentieth of a. second per character is required or twelve hundred characters per minute may be transmitted. As this speed is rather high for manually operated keyboards, a tape may be used if desired to send the impulses over the transmitting medium in order to keep it fully occupied. The tape perforating and sending mechanism may be of similar type to those used in ordinary practice and those skilled in the art can readily see the application without detailed explanation;

The several taps 21C on the inductance 21 connected to the groups, as shown, will tune the circuit to resonate at eight different frequencies, al-

ready referred to as group frequencies, and twelve different character frequencies. connected as an oscillator with the coil 213 as the feed-back device, feeding energy to the grid from the tuned-plate circuit. The tube 43 acts as an amplifier for all the frequencies produced, and the resistance coupling means shown ,has the property of passing all the frequencies generated with substantially uniform gain to the transformer 44.

The key 03, as already explained, is on the transmitting apparatus for manual operation as .a capital shift key; that is, for each individual key in a group there is on the receiving end of the system a representation of two characters, and the change from one character to the other is accomplished at the sending end of the system by the ordinary typewriter. This key is of the eightspring type functioning with the effect of a double throw four pole switch to change taps on the inductance 21. The switch operated by the key 83 is shown by symbol in neutral position, but when in the upper or normal position any one of four group frequencies will be transmitted, but when in the depressed position any one of another set of group frequencies will be transmitted.

The contact I is used to complete the circuit to the controlling means of the oscillator at 40 and as plate return lead to tube 4| and the spacer arrangement. The contact 8 is normally closed and, together with the contact 9, forms the group frequency fixing circuit, as it closes the circuit through one of the various taps on the tuning inductances. The contact I0 is used to complete the group position circuit through one ofthe various tuning condensers 2839. In the Figure 2 the spacing contact is closed and the other two circuits are open. In the Figure 3 the spacing 'circuit is open but the group circuit is closed.

In the Figure 4 the spacing and group circuits are both open,,but the group position circuit'is closed. p

In the Figure 5 the numeral 45 shows the line which is connected to numerous coils, such as 46, 60, and 19. There are eight coils 46 which feed energy into the group selecting arrangement in which 41 is the tuning coil and 48 is the tuning condenser. The numeral 49 shows the tube shunted across the tuned circuit with it's grid biased by the battery 50 or similar well known means, with the by-pass condenser 5|. This tube 49 is of the thyratron type and its plate current is started by excitation of the grid but continues after .the grid voltage returns to the bias point.

The plate of the group frequenci selector tubes the improved form as already explained. The

primary coil 60 delivers energy to the tuned circuits formed of inductance 6| and the condenser 62. The thyratron tube 63 is connected across this tunedcircuit as shown and the grid of the tube 63 is biased by the battery 64 and the bypass condenser 65.

The cathode of this tube 63 is connected to a group position line of solenoids II and similar The tube 4| is tubes and tuning circuits are connected to similar group position lines, such as 66 toI'l'l, respectively. The resistance '18 is used to shunt the tube 63 and the entire set of relay solenoids in order to allow the tube 49 to start, but does not allow enough current to pass to operate the relays, the current allowed to pass being just sumcient to ionize the gas in the tube 49 and to insure thyratron action. Similar resistances are used for each of the other group relays. The primary coil I9 is used to transfer energy to the tuning circuit formed of coil and the condenser 90. The tube 6|.is shunted across this tuned circuit and its grid is biased by the resistor 9| and the by-pass condenser 92. This tube 8| is an ordinary amplifying tube inwhich the grid retains control at all times and can stop the plate current as well as start it. In the plate circuit of this tube 8| is a relay at 93 which is adapted to operate contacts 94.

In the Figure 6 the numeral |0| designates a complete sending set such as is shown in the Figure 1, while the numeral I02 designates a receiving arrangement as illustrated more in detail by the Figure 5. The numeral I04 designates the connecting line, while I03 designates a re.- peating arrangement for increasing the amplitude of attenuated signals in the usual manner.

In the Figure 7 the numeral I05 designates a sending arrangement with an amplifier to bring the signals up to high power, while I06 designates a carrier frequency transmitter and modulator for putting the signals asmodulated radio frequency on the antenna I09. A receiving and de-modulating arrangement is shown at I01, and the low without necessarily synchronizing the signals. It

also will be noted that, the novel method of transmitting two or more impulses by a single operation of a key, provides for unlimited speed in the transmission of the characters, and that this speed may be accomplished also by the use of perforated tape contacts. And it will be noted further that, in the transmission of the characters by this improved system, no coding is required for secrecy; for great secrecy is assured alone by the use of two signals for one character transmitted, it being impossible to interpret either the group-selecting signal or the group position signal, both of which are signals for the mere selection and operation of somemechanical movement actuated by electrical impulses.

In Fig. l of the drawings, the windings flaand 21b of the transformer 21 are shown as having substantially the same number of turns but it is to be understood that the number of wins of the secondary or the primary may be changed to provide any desired ratio of transformation and the iron' core of the transformer may be eliminated Where it is desired to operate at high frequencies.

In the specification above, the term thyraton has been used to denote a discharge tube of the mercury vapor'type including at least a cathode and anode and a control grid. In this tube an electron emission is obtained from a cathode consisting of. an oxide coated filament or other type of electron emitter. The mercury in the tube produces a vapor pressure depending upon the coolest part of the tube. Electrons emitted by tial of sufiicient valuev with respect to the cathode will prevent the occurrence of a discharge. Once the discharge has started, the grid potential has no appreciable effect on the anode current; control is restricted to the grid only when the discharge ceases long enough for the mercury to deionize.

The invention herein described may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

I claim:

1. A printing telegraph system including a keyboard, multipleswitches operated by keys, an oscillator the frequency of which is altered by the switches, a separate oscillator for the generation of a spacing frequency, a transmitting line connected to parallel selecting tuned circuits, thyratron tubes shunted across these tuned circuits, solenoids in series with the thyratron plate circuits and adapted to operate type-bars, and spacing means actuated by a back-contact of the transmitting key which thereby sends a special frequency signal over the line and operates a tuned relay to open the plate circuit of the thyratron tubes and restores the type -bars to nonprinting position.

2. A' printing telegraph system having a keyboard with one character key for each two characters, a shift key for selecting either one of the two characters, three single-throw switches operated by each character key, a four pole doublethrow switch operatedby the shift key, a tuned circuit whose resonant frequency is altered by said switches, an oscillator whose frequency is set by the tuned circuit, an amplifier for increasing the amplitude of a signal, a line between the transmitting apparatus and a receiving apparatus adapted to receive a transmitted signal and having tuned circuits arranged to oscillate in resonance with the received signals, tubes shunted across the tuned circuits and arranged to control the current flow in one of a multiplicity of solenoids to operate a type-bar with which the particular solenoid is associated responsive to the conjoint energization of two of said tubes.

3. In a device for telegraphically printing characters at a distance in which a plurality of circuit opening and closing keys are employed at a transmitting station and a plurality of groups of frequency selective thyratrons are employed at a receiving station, the method of energizing a selected pair of said thyratrons which comprises translating the movement of a key at the transmitting station into a signal of successive impulses of alternating current of different frequencies, rendering one of said thyratrons of one group conductive responsive to one of said impulses and rendering one of said thyratrons .of

another group conductive responsive to the con- Joint action of another of said impulses and the precedent energization of one of the thyratrons of the first mentioned said group.

a. In a printing telegraph transmitter having character keys, means for transmitting a plurality of frequencies in succession responsive to the depression of any character key comprising an oscillation generator and means forconnecting into the frequency determining circuit of said oscillation generator selected values of inductance and capacity at a plurality of degrees of depression of said keys.

5.-In a printing telegraph transmitter having character keys, means for transmitting a plurality of frequencies in succession responsive to the depression of any character key comprising an oscillation generator and means for connecting intothe frequency determining circuit of said oscillation generator selected values of inductance and capacity at a. plurality of degrees of depression of said keys, and means for transmitting a spacing frequency responsive to the return to normal position of any one of said keys.

6. In a telegraph printer in which a character is printed responsive to the receipt of 'a plurality of successively transmitted different frequencies,

each of which is included in the control circuit or a thyratron tube and means responsive to the energization of any one of a first group of said thyratron tubes responsive to the receipt of a first frequency for preparing a circuit for a second group of said thyratron tubes, and means for energizing one of the thyrathon tubes of said second group responsive to the receipt of a second frequency. I

7. In a telegraph printer in which a character is printed responsive to the receipt of a plurality ofsuccessively transmitted different frequencies, a plurality of parallel frequency selective circuits each, of which is included in the control circuit of a thyratron tube and means responsive to the energization of any one of a first group of said thyratron tubes responsive to the receipt of a first frequency for preparing a circuit for a second group of said thyratron tubes, and means for energizing one of the thyratron tubes of said second group responsiverto the receipt of a second frequency, and means comprising a solenoid included in the circuit of said thyratrons for actuating a character printing device.

8.In a printing telegraph system wherein a character is printed responsive to the receipt of a series of successively transmitted signals of more than one frequency, a plurality of parallel connected frequency selective circuits, each circuit being so proportioned as to resonate to currents of characteristic frequency, means responsive to the receipt of a first frequency of a series for closing a point in a circuit corresponding to the group to which the signal belongs, means responsive to the receipt of a second frequency of the series for closing a point in a circuit corresponding to the sub-group to which the signal belongs, and means responsive to the receipt of all of the frequencies of the series for energizing a solenoid corresponding to the characterof said series.

. SIDNEY Z. BEAR. 

